Scintillators are materials that emit flashes or pulses of light when they interact with ionizing radiation. Scintillator crystals are widely used in radiation detectors for gamma-rays, X-rays, cosmic rays, and particles characterized by an energy level of greater than about 1 keV. It is possible to make radiation detectors, by coupling the crystal (or scintillator) with an element for detecting the light produced by the crystal when it interacts, or “scintillates,” when exposed to a source of radiation. The photo-detector produces an electrical signal proportional to the intensity of the scintillation (or light pulses received from the scintillator material). The electrical signal is then processed in various ways to provide data on the radiation.
Gamma-ray spectroscopy is an important capability for radioactive isotope identification and is typically accomplished using inorganic scintillators or inorganic semiconductors. Recent advances have resulted in exceptional spectroscopic performance from both of these classes, yielding 662 keV energy resolution values of less than 3% for scintillator and less than 1% for semiconductors. However, high detector costs and low production yields remain as two significant shortcomings that prohibit their replacement of NaI(Tl) scintillators in large-scale applications.
Organic-based plastic and liquid scintillators have been proposed and investigated as an alternate paradigm that foregoes high-resolution gamma-ray spectroscopy in favor of high-efficiency detection. Plastic compounds provide a low-cost solution for large-volume scintillators. Plastic scintillators deployed in various applications including portal monitoring applications have been shown to be vulnerable to environmentally-induced aging processes that are detrimental to their optoelectronic performance. Light scattering “fog,” comprising condensed water vapor beyond the saturation limit of the plastic is one example of an aging defect often encountered in plastic scintillators.